Optimizing lignin cationization: Unveiling the impact of reaction conditions through multi-response analysis

Journal article, 2025

Lignin, a natural and abundant biopolymer, holds great potential for cosmetic applications. However, its limited solubility and inherently negative charge restrict its use in certain formulations. This is particularly relevant for hair conditioning, where a positively charged polymer is preferred to effectively treat negatively charged damaged hair. To overcome this limitation, lignin extracted from acacia wood residues was chemically cationized, through an etherification reaction, using 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) as cationization agent. The cationization process was optimized through a full factorial design of experiments aiming to maximize both the degree of substitution (DS) and ζ-potential of the lignin derivatives, thereby obtaining more positively charged derivatives. The reaction parameters temperature and CHPTAC-to-lignin molar ratio were selected as independent variables to be optimized. Results revealed that the reaction temperature is the most relevant parameter for lignin cationization, showing a significant positive influence on lignin modification, while the CHPTAC-to-lignin ratio has no significant impact. Under optimal conditions, soluble derivatives with a DS of 0.61 ± 0.03 and a ζ-potential of 18.79 ± 0.30 mV were obtained, confirming the success of the reaction. This straightforward and efficient approach enhances acacia's lignin solubility and charge properties, broadening its application potential. In particular, it offers a promising alternative for hair conditioning, thus contributing to the sustainable development of bio-based cosmetic ingredients.